1. Field of the Invention
The present invention relates in general to a full rotary hook for a sewing machine and in particular to such a hook suitable for use with a pattern or embroidery sewing machine.
2. Related Art Statement
A conventional full rotary hook shuttle for such use includes (a) a generally cylindrical hook base having a point of hook, an inner circumferential surface, and a guide groove provided in the inner circumferential surface, and (b) a generally cylindrical bobbin-case holder having an inner circumferential surface, an outer circumferential surface and a part-circumferential rail provided on the outer circumferential surface, the bobbin-case holder being supported by the hook base such that the bobbin-case holder is freely rotatable relative to the rotary hook while the rail is guided by the guide groove.
However, this hook has no means for guiding a sewing needle with a top or upper thread. The hook produces no problem when it is used in a common sewing machine in which a work fabric or cloth is fed in an unchangeable direction. However, when the hook is used with a pattern or embroidery sewing machine in which directions in which a work cloth is fed are often changed, the hook provides a problem that a point of hook fails to catch a loop of the upper thread, producing a skipping stitch or a thread breakage, if continuous feeding of the work cloth is carried out, or if double fabric sewing is carried out using a thick fabric or cloth even by intermittent feeding of the work cloth. The reason for this problem is that the sewing needle is bent slightly away from the point of hook by being pulled by the cloth, depending upon the direction in which the cloth is fed, thereby increasing the possibility that the point of hook fails to catch the upper thread.
For solving the above problem, it has been proposed, as indicated in two-dot chain line in FIG. 3, to provide, between a throat plate 100 and a bobbin-case holder, 20, a needle guide 102 for preventing a sewing needle 2 from being displaced away from a point of hook 16. Alternatively, it has also been proposed to form, in place of a needle hole 104 concentric with the needle 2, a needle hole 106 eccentric with the needle 2 in the throat plate 100, so that the eccentric hole 106 serves for guiding the needle 2.
However, even where these needle guides 102, 106 are used, they come into contact with the upper thread, thereby exerting resistance to the same and reducing tightness of the stitches formed.